Questions about the simplest and most abundant element in the Universe.

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Population of excited H levels in a Strömgren Sphere

In chapter 2.2 of Astrophysics of Gaseous Nebulae and AGN Ostriker and Ferland claim that, as far as ionization is concerned, one can assume all atoms to be in the ground state in a Strömgren Sphere ...
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What are the implications if the Sun was formed in a warm nebula?

Molecular oxygen O2 has been found on comet 67P/C-G in a ratio of 3.8% to water, which is much higher than expected. An explanation proposed is that the Solar System formed from a molecular cloud ...